The present invention relates to radiation polymerisable compositions and in particular to compositions curable with ultraviolet light (UV) or electron beam (EB) radiation or elemental sources such as cobalt with its gamma rays, strontium 90 or caesium 137 and the like.
Radiation polymerisable compositions are used in a range of applications including coatings, inks and films. Radiation polymerisable compositions typically contain acrylate or methacrylate monomer and a prepolymer and when UV curing is to be used a photoinitiator or photosensitiser is required.
Attempts have been made to increase curing efficiency and reduce the need to use photoinitiators by increasing the sensitivity of compositions however in many cases this reduces their stability and also reduces the options available to the end user.
The present invention provides a radiation polymerisable composition comprising:
(A) a donor/acceptor component for forming a charge transfer complex said component being selected from the group consisting of:
(i) a bifunctional compound having an electron donor group and an electron withdrawing group and a polymerisable unsaturated group;
(ii) a mixture of (a) at least one unsaturated compound having an electron donor group and a polymerisable unsaturated moiety; and (b) at least one unsaturated compound having an electron acceptor group and a polymerisable unsaturated group; and
(B) a binder polymer composition.
The binder polymer in contrast to the donor acceptor composition will not interact with the components of the donor/acceptor complex to form a change transfer complex.
In contrast with the donor/acceptor component which has a relatively low molecular weight, typically if no more than about 1100 and has a high proportion of unsaturation to readily form donor accepter charge transfer complexes the binder polymer has a significantly higher molecular weight and low level of residual unsaturation. The molecular weight of the binder polymer is higher than 1100, preferably greater than 2000 or a highly viscous material and most preferably greater than 5000. The binder polymer is typically a solid or a highly viscous material at room temperature though in use in the composition of the invention it will typically be dissolved in the other components. The binder polymer does not readily complex with donors such as triethylene glycol divinyl ether (DVE-3) or acceptor to provide a cured film on its own in the absence of a donor/acceptor complex.
Suitable donor/acceptor complexes for use in the present invention are disclosed in U.S. Pat. No. 5,446,073 by Jonsson et al. We have found that such complexes in the absence of a binder polymer can not be adequately controlled for commercial use. Further their use generally requires newly developed excimer lasers which are not commonly used in current industrial UV curing system.
The compositions of the invention by contrast allow rapid cure and yet allow their use to be controlled to provide useful industrial application in many cases allowing UV curing in the absence of photoinitiators and yet are relatively inexpensive.
The compounds employed to provide the charge transfer complex can be ethylenically unsaturated or acetylenically unsaturated. When the complex is from two or more compounds, typically, the double bond molecular ratio of the electron donating compound to the electron withdrawing compound is about 0.5 to about 2, and more typically about 0.8 to about 1.2 and preferably about 1:1. In contrast the binder polymer has a ratio typically less than 0.5 and preferably no more than 0.3. It will be understood that the double bond ratio of the binder may be different in different donor/acceptor complexes and remain inert with respect to donor/acceptor interaction under the conditions used. The complexes employed for the present invention are stable under normal conditions.
In particular, the compositions do not spontaneously polymerise. The strength of both the donor and acceptor groups are not to the high level that could result in spontaneous polymerisation. Instead they polymerise under the influence of the necessary ultraviolet light or ionising radiation.
The charge transfer complex formed from the donor/acceptor is capable of absorbing light having a wave-length that is longer than the longest wavelength in the spectrum of light absorbed by the individual donor and withdrawing groups used to form said complex. The ultraviolet light is thus absorbed by the charge transfer complex rather than by individual groups or components forming said complex. This difference in absorptivity is sufficient to permit the polymerisation of said complex to proceed by absorbing light.
In the terms of commercial utilisation, the complex typically absorbs light which has a wavelength that is about 10 nanometers longer than the shortest wavelength in the spectrum of light absorbed by the individual donor and withdrawing groups or components. This facilitates tailoring the spectral output from the ultraviolet light source to assure the desired polymerisation.
The complex should, on initial exposure to UV, lead to radicals which can initiate free radical polymerisation. In addition to UV, the polymerisation can also be achieved by the use of ionising radiation such as gamma rays or electrons from an electron beam machine. This process can be achieved to workable radiation doses and in air.
The electron withdrawing and electron donating compounds can be represented by the following formula:
(A)nxe2x80x94R and (D)nxe2x80x94R, respectively;
wherein xe2x80x9cnxe2x80x9d is an integer preferably from 1 to 4, xe2x80x9cRxe2x80x9d is the structural part of the backbone. xe2x80x9cAxe2x80x9d is the structural fragment imparting acceptor properties to the double bond.
This is selected from the groups outlined in the Jonsson et al Patent (U.S. Pat. No. 5,446,073) and consists of maleic diesters, maleic amide half esters, maleic diamides, maleimides, maleic acid half esters, maleic acid half amides, fumaric acid diesters and monoesters, fumaric diamides, fumaric acid monoesters, fumaric acid monoamides, exomethylene derivatives, itaconic acid derivatives, nitrile derivatives of preceding base resins and the corresponding nitrile and imide derivatives of the previous base resins particularly maleic acid and fumaric acid.
Typical electron withdrawing compounds are maleic anhydride, maleamide, N-methyl maleimide, N-ethyl maleimide, N-phenyl maleamide, dimethyl maleate, diethyl and dimethyl fumarate, adamantane fumarate and fumaric dinitrile. Analogous maleimide, N-methyl maleimide, N-ethyl maleimide, phenyl maleimide and their derivatives can also be used.
Examples include polyethylenically unsaturated polyesters, for example, polyesters from fumaric acid and maleic acid or anhydrides thereof.
xe2x80x9cDxe2x80x9d is the structural fragment imparting donor properties to the double bond and is selected from the groups outlined below. Examples of component D are provided in the Jonnson et al U.S. Pat. No. 5,446,073 and includes vinyl ethers, alkenyl ethers, substituted cyclopentanes, substituted cyclohexanes, substituted furanes or thiophens, substituted pyrans and thiopyrans, ring substituted styrenes, substituted alkenyl benzenes, substituted alkenyl cyclopentanes and cyclohexenes. In the styrene systems, substituents in the ortho- and para-positions are preferred. Unsaturated vinyl esters like vinyl acetate and its derivatives can also be used.
In addition, polyfunctional, that is, polyunsaturated compounds including those with two, three, four or even more unsaturated groups can likewise be employed.
With respect to the ethers, mono-vinyl ethers and di-vinyl ethers are especially preferred. Examples of mono-vinyl ethers include alkylvinyl ethers typically having a chain length of 1 to 22 carbon atoms. Di-vinyl ethers include di-vinyl ethers of polyols having for example 2 to 6 hydroxyl groups including ethylene glycol, propylene glycol, butylene glycol, 3 methyl propane triol and pentaerythritol.
Examples of some specific electron donating materials are monobutyl 4 vinylbutoxy carbonate, monophenyl 4 vinylbutoxy carbonate, ethyl vinyl diethylene glycol, p-methoxy styrene, 3,4 dimethoxy propenyl benzene, N-propenyl carbazole, monobutyl 4 propenyl butoxy carbonate, monophenyl 4-propenyl butoxy carbonate, isoeugenol and 4-propenylanisole. Vinyl acetate is also active especially with monomers like maleic anhydride and the maleates.
Typical bifunctional compounds containing both acceptor or withdrawing groups and a donor group can be used and are listed in the Jonnson et al patent. Examples of suitable bifunctional compounds include those made from condensing maleic anhydride with 4-hydroxybutyl vinyl ether and the like.
A further limitation of the donor/acceptor composition disclosed in Jonnson is the relative expense of many donor/acceptor components relative to the UV curable monomers currently used in industry. Among the less expensive acceptor components is maleic anhydride (MA) which can be combined with a donor, which may be a vinyl ether such as triethylene glycol di-vinyl ether, to provide a cured film.
In practical commercial situations, the above system suffers from several disadvantages, especially when used with current industrial lamp systems on line. This problem is apparent for example in clear coating applications. It would be an advantage for companies to be able to use the current commercial lamp systems with donor/acceptor charge transfer complexes described above, otherwise the addition and installation of more efficient lamps becomes very expensive and limits the application of the process. Newly developed excimer sources such as the Fusion V.I.P. system will cure most of the systems discussed above if they can be converted into stable films prior to curing. These V.I.P. systems are expensive and their ready availability is required, however there are currently few V.I.P. commercial facilities on stream. The present CT system in the Jonnson et al patent possesses a number of limitations in practical use even with the V.I.P. lamp system. Thus MA, although the cheapest of available donors, suffers from the disadvantage of solubility when used with the less expensive donors like DVE-3. This problem causes the MA to crystallise out of solution when the DA mixture is at temperatures of 25xc2x0 C. or lower, i.e. common room temperature. Thus storage and transit become a problem under these conditions and the mixture to be used must be reheated carefully before application to redissolve the MA. This heating operation can give rise to significant dangers since the CT complex is very temperature sensitive and can exothermically explode if the heating is not performed carefully. This heating operation would be difficult in commercial environments. In addition, at the time of application, the mixture needs to be at temperatures above 25xc2x0 C. otherwise coating is a problem and so the line and the mixture need to be continuously heated for application. MA has another disadvantage in this work due to its volatility and odour, which is unacceptable for certain applications at the level of MA used. The problem is not confined to the DVE-3 complex. The other ethers behave in a similar manner and are more expensive than DVE-3.
Of the available acceptors other than maleates, the maleimides are the most reactive such as the alkyl derivatives such as N-hexyl maleimide. The problem with the maleimides is their toxicity and thus extreme caution must be exercised in commercial situations with such materials. Their use is not therefore favoured industrially.
A problem also exists with the most economically available donors such as DVE-3. These materials have very low viscosity which can render the final coating formulations unsatisfactory for many commercial applications since the coatings can either run off or be absorbed by the substrate. We have found that the viscosities of such formulations need to be increased significantly before the coatings are suitable for industrial use.
The binder polymer such as polyester alkyd and vinyl ether polymers have been found to improve the cure speed particularly of MA/DVE-3 and similar complexes and to improve the stability of the complexes prior to cure. A further advantage of such binder polymers is that they reduce significantly the odour of MA/DVE-3 complex and related complexes.
The weight ratio of donor/acceptor complex to said binder polymer is typically in the range of 1:99 to 95:5 with from 30:70 to 70:30 being preferred and 60:40 to 40:60 being most preferred.
In a further preferred embodiment the acceptor comprises a mixture of maleic anhydride and an ester selected from the group consisting of the mono- and di-methyl and ethyl maleic esters. While the weight ratio of ester to MA can be up to 99:1 we have found that the best rate of cure is provided if the ratio of ester to MA is less than 75:25 and more preferably 75:25 to 25:75. Most preferably a diester is used and the ratio of diester to MA is in the range of 60:40 to 40:60.
Surprisingly we have found that the use of the binder polymer gives stability to compositions such as maleic anhydride and increases viscosity of composition. A particular advantage is the improved solubility of the accepter component particularly maleic anhydride and the donor particular ethers including vinyl ethers such as triethylene glycoldivinylether (DVE-3). The presence of the binder also leads to improved complex stability at a range of temperatures especially room temperature at which most applications occur.
The preferred binder polymers are selected from unsaturated polyesters, vinyl ethers, polystyrene polyarylamides, polyvinyl acetate, polyvinyl pyrrolidones, acrylonitrile butadiene styrene, cellulose derivatives and mixtures thereof.
Polyesters and polyvinyl ethers are preferred and most preferred are alkyd polyesters prepared from copolymers of a polyol such as alkylene glycol or polyalkylene glyol and anhydride such as maleic anhydride phthalic anhydride or mixture thereof. One specific example of the preferred polyester alkyd is available from Orica Ltd Australia and is prepared from propylene glycol, phthalic anhydride and maleic anhydride. An example of the less preferred vinyl ether polymer binder is Vectomer 1312 brand vinyl ether polymer of Allied Signal, USA.
If photoinitiators are used for example in highly pigmented systems, suitable examples of photoinitiators may include benzoin ethers such as xcex1,xcex1-dimethoxy-2-phenylacetophenone (DMPA); xcex1,xcex1-diethoxy acetophenone; xcex1-hydroxy-xcex1 xcex1-dialkyl acetophenones such as xcex1-hydroxy-xcex1, xcex1-dimethyl acetophenone and 1-benzoylcyclohexanol; acyl phosphine oxides such as 2,4,6-trimethylbenzolyl diphenyl phosphine oxide and bis-(2,6-dimethoxybenzoyl)-2,4.4-trimethylphenylphosphine; cyclic photoinitiators such as cyclic benzoic methyl esters and benzil ketals; cyclic benzils; intermolecular hydrogen abstraction photoinitiators such as benzophenone, Michlers ketone, thioxanthones, benzil and quinones; and 3 ketocoumarins. Typical of such photoinitiators are the Ciba Geigy range of Irgacure 819, 1800, 1700 and the like, also Darocure 1173.
In the case of clear coatings a photoinitiator may not be necessary or may be used in minor amounts of up to 2% if desired. Pigmented systems may use a photoinitiator with the amount required depending on the level of pigmentation. Amounts of PI may be up to 6% by weight are typical.
The photoinitiator component may also be used in combination with an amine coinitiator particularly a tertiary amine coinitiator. This is particularly preferred in the case of the intermolecular hydrogen abstraction photoinitiators such as benzophenone. The amine is generally triethanolamine or an unsaturated tertiary amine such as dimethylaminoacrylate, diethylaminoethylacrylate or the corresponding methacrylates. An amine/acrylate adduct such as that sold under the trade name Uvecryl 115 by Tollchem Pty Ltd Australia is also useful as a coinitiator. Where the unsaturated amine is used it will of course contribute to the monomer or polymer component. If the latter components are used as PI, care must be exercised in formulation to show that the components of the original CT complex do not interfere and slow the cure.
Oligomer acrylates such as epoxy acrylate, urethane acrylate and polyester acrylate may be used if desired. In addition acrylate monomers may also be used as additives especially the multifunctional acrylates like tripropylene glycol diacrylate (TPGDA) which improve cross linking and are also used to speed up cure of oligomer acrylates and UV cure.
Such materials are supplied by Sartomer, UCB and the like. Again, if the acrylate monomers are incorporated Pt is needed to achieve cure. The level of PI is significantly high being of the order of at least 1% by weight of total polymer.
Finally mixtures of acrylate oligomer with acrylate monomer (e.g. TPGDA) may also be used in combination instead of either, separately. Again in this instance PI will be needed at the levels previously mentioned for oligomer acrylate and acrylate monomer when used individually.
Examples of ethylenically unsaturated monomers that can be used include unsaturated carboxylic acids and esters particularly acrylate and methacrylate esters.
Acrylamides, allyl compounds such as diallyl phthalate, maleimide and its derivatives; maleic acid, maleic anhydride, fumaric acid, and their esters and amides, and other unsaturated compounds such as benzene, di-vinyl benzene, N-vinylcarbazole and N-vinylpyrrolidone.
The preferred monomers are monomers comprising a plurality of acrylate or methacrylate functional groups which may be formed, for example, from polyols or the like. Examples of such multifunctional acrylates include trimethylolpropane triacrylate (TMPTA) and its ethoxylated derivative, neopentyl glyol diacrylate, tripropyleneglycol diacrylate (TPGDA), hexanediol diacrylate (HDDA) and polyethyleneglycol diacrylates such as that formed from PEG 200. The molecular weight of the monomer will typically be less than 2000.
The composition used in the method of the invention may include a thermal polymerisation inhibitor such as di-t-butyl-p-cresol, hydroquinone, benzoquinone or their derivatives and the like. Di-t-butyl-p-cresol is preferred. The amount of thermal polymerisation inhibitor is typically up to 10 parts by weight relative to 100 parts by weight of the resin component.
The composition may contain an ultraviolet light stabiliser which may be a UV absorber or a hindered amine light stabiliser (HALS). Examples of UV absorbers include the benzotriaziols and hydroxybenzophenones. The most preferred UV stabilisers are the HALS such as bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate which is available from Ciba as TINUVIN 292 and a poly[6-1,-1,3,3-tetramethylbutyl)imino-1,3,5-triazin-2,4-diyl] [2,2,6,6-tetramethyl-4-piperidyl)imino] hexamethylene [2,2,6,6-tetramethyl-4-piperidyl)imino] available from Ciba under the brand name TINUVIN 770. The amount of UV stabiliser that is effective will depend on the specific compounds chosen but typically up to 20 parts by weight relative to 100 parts by weight of resin component will be sufficient.
The UV stabiliser may be used simply to provide UV protection to the coating applied in accordance with the invention in which case up to 10 parts by weight will generally be adequate and in the case of HALS 0.05 to 5 parts is preferred. In some embodiments however it may be desirable to use a high concentration of stabiliser particularly where UV protection is also to be provided for the substrate to which the coating is to be applied.
If flame retardency is desired the composition used in the process of the invention may include one or more flame retarding additives. Preferred examples of such additives may be selected from the following:
a: xe2x80x9cFYROL 76xe2x80x9d*(with and without free radical catalyst such as tertiary butyl hydroperoxide, cumene peroxide or ammonium persulphate);
b: xe2x80x9cFYROL 51xe2x80x9d*
c: xe2x80x9cFYROL 6xe2x80x9d*and/or xe2x80x9cFYROL 66xe2x80x9d*with and without catalyst; PRODUCTS OF AKZO CHEMICALS LTD.;
d: xe2x80x9cPE-100xe2x80x9d and xe2x80x9cW-2xe2x80x9d (EASTERN COLOR CHEMICALS P/L) of the USA;
e: xe2x80x9cPROBANxe2x80x9d *with and without catalyst such as ammonia or an amine; *an ALBRIGHT AND WILSON Aust. PTY LTD. PRODUCT;
f. xe2x80x9cPYROVATEXxe2x80x9d *with and without catalyst; *a CIBA GEIGY Aust. PTY LTD. PRODUCT;
g: xe2x80x9cPYROSETxe2x80x9d *xe2x80x9cTPOxe2x80x9d and xe2x80x9cTKOWxe2x80x9d with and without catalyst; *PRODUCTS OF CYANAMID Aust. PTY. LTD.;
h: simple phosphates such as mono, di, and triammonium ortho phosphates and their alkali metal equivalents;
i: alkali metal and ammonium sulphamates;
j: alkali metal and ammonium range of poly phosphates;
k: ammonium sulphates;
l: alkali metal and ammonium chromates and dichromates;
m: alkali metal carbonates;
n: alkali metal tungstate;
o: boric acid and borax;
p: organo phosphorus or organo boron compounds;
and mixtures of two or more of the above.
The preferred amount for each system may be determined by experiment. When the additives are used with the resin, the finished product may be fire retarded in accordance with Australian Standard AS1530 Parts 2 and 3.
Particularly preferred fire retarding additives are Fyrol 76, Fyrol 51, PE-100 and W-2 and mixtures thereof. The other flame retardants in xe2x80x9caxe2x80x9d to xe2x80x9cpxe2x80x9d are best used for specific applications and as with all the above retarding additions, their conditions of use are determined by the equivalent level of phosphorus present in the finish. When the Fyrols or PE-100 or W-2 are used, the amounts are 1 to 50% based on the mass of resin solids with 2 to 20% preferred. Generally, the equivalent proportion of elemental phosphorus (and boron if used in combination) in the combination to a level of 4.0% P is needed to achieve the required flame retardency. However, significantly less may be needed depending on the substrate material. For example some materials may need only 2.0% P. In such cases the exact levels of phosphorus containing compound required are determined exactly by experiment. Thus the range covered from 0.02 to 15% of elemental phosphorus based on the mass of the substrate material to be treated may be used, with 0.2 to 4.0% P being the preferred range to achieve flame retardency. Flame retardants are particularly useful where the coating is to be applied to a textile or natural or synthetic fibre.
We have also found that superior coating properties are provided when the coating is applied to a wet substrate.
Additional additives which may be used in the formulations are wetting agents, water if required, matting agents, solvents if required, fluorinated additives and silanes to improve gloss and flow, surfactants, levelling agents, fillers, pigments, slip agents and defoaming agent.
A further aspect of the current invention is the ability to reduce the gloss of the clear coating to give either a matt or semi gloss UV cured finish. This is accomplished by adding to a 1:1:2 mol. ratio mixture of MA, DVE-3, PE 4% calcium carbonate and 4% of pyrogenic silica (Acermaft OK 412, De Gussa) with 4% Irgacure 819 to give a semi gloss UV finish. If the calcium carbonate is increased to 6% and the Irgacure 819 to 8% a matt UV cured finish is achieved.
The invention further provides a process for preparing a radiation curable composition comprising forming a mixture of:
(a) at least one unsaturated compound having an electron donor group and a polymerisable unsaturated moiety; and
(b) at least one unsaturated compound having an electron acceptor group;
in the presence of a binder polymer to form a donor/acceptor charge complex from said components (a) and (b).
The process may further include addition of one or more further components such as the photoinitiator, monomer, pigment and flame retarders in accordance with respective components described above.
The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention.